There are many occasions when it is desirable to apply a torque to a work piece (such as nuts, bolts, and in-line hydraulic fittings) in order to, for example, rotate the work piece with respect to a threaded member. Two well-known tools for rotating work pieces are ratchet wrenches and open-ended crescent wrenches. Ratchet wrenches are typically close-ended devices that completely encircle the work piece and are thus installed on the work piece from the top (or bottom, depending upon the orientation of the work piece). Open-ended wrenches can be installed from the side of the work piece.
Open-ended wrenches are useful in small work spaces where there may only be sufficient room to install the wrench from the side. In some situations, confined work spaces may provide insufficient space to accommodate the ratchet mechanism of close-ended ratchet wrenches. Open-ended wrenches are also useful in tightening/loosening in-line fittings of hydraulic or fuels lines, which are configured to receive a wrench from the side.